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Testing of a concrete sealer using the rapid chloride permeability technique.

Introduction and Background

Sealers and penetrants are used primarily to prevent the corrosion of reinforcing steel caused by aggressive chloride ions when concrete bridge members are exposed to deicers or marine environments. The effectiveness of sealers and penetrants in preventing chloride ions from entering the concrete matrix depends on their own ability to penetrate--and thereby protect--the matrix. This ability is largely dependent on the matrix's void system and quality. For normal quality bridge concrete, the depth of penetration by most sealers is not significant unless the concrete has been thoroughly dried by continuous heating at elevated temperatures. In those circumstances, the sealers would penetrate much as they do in the polymer impregnation process (in which the polymer replaces the evaporated water from the heated concrete matrix).

Manufacturers and distributors claim that their sealants and penetrants can penetrate into the concrete matrix. To evaluate such claims, the Federal Highway Administration (FHWA) tested one type of sealer product under a realistic outdoor environment at the Turner-Fairbank Highway Research Center (TFHRC). The supplier claimed a penetration of 102 to 127 mm (4 to 5 in) into the concrete from the surface. The product is an aqueous solution of sodium silicate containing specific activators to achieve penetration and chemical bonding to the cementitious part of concrete. The experiment was designed to evaluate:

* The effectiveness of the penetrant in reducing the permeability of hardened concrete.

* The depth of penetration of the sealant into the concrete.

Study Design

A piece of a reinforced concrete bridge deck from the I-395 spur ramp "D" over Howard Street in Baltimore, Maryland, was used to test the sealer. This tined deck section was taken from a negative moment region of the span directly over a pier. The bridge was constructed in 1980-81 and recently removed to permit construction of a new baseball stadium. The total area of the removed deck section was approximately 12.2 [m.sup.2] (40 [ft.sup.2]. The deck section was furnished to the FHWA in January 1991; it was subsequently stored on the TFHRC grounds without a cover or other protection.

The weather for the 5 days prior to sealer application was generally sunny. The temperature at the time of treatment was moderate. The reinforced concrete slab section was sandblasted to remove dirt, oil, and other loose debris and also to expose the aggregate slightly; the goal was to provide a clean surface for the application of the sealer (figure 1). Only 7.6 [m.sup.2] (25 [ft.sup.2]) of the prepared section was used in the study; this was subdivided into five equal 0.6 by 0.8 m (2 by 2.6 ft) sections (figure 2). These five sections were treated as follows:

* Section 1: Concrete surface was wetted and then air-dried; 250 g of the sealer was then then brushed on in two coats.

* Section 2: Same as section 1, except that after 1 week, section 2 was sand blasted heavily to eliminate the surface sealing and expose a fresh concrete surface.

* Section 3: Concrete surface was not wetted; 250 g of the sealer was brushed on in two coats.

* Section 4: Control section (no sealer applied).

* Section 5: Concrete surface was wetted and then air-dried; sealer was sprayed instead of brushed on. This application procedure is the one recommended by the manufacturer.

Four full-depth nominal 102-mm (4-in) diameter cores were then extracted from each section. An additional core was from section 2 for a total of 17 cores taken from the four sections. All of the cores were sawed into 51-mm (2-in) thick concrete disks for testing by American Association of State Highway and Transportation Officials (AASHTO) standard T-277, "Rapid Determination of the Chloride Permeability of Concrete." [1] (1)


A 6.35-mm (.25-in) segment of the top concrete surface was sliced from two of the five cores from the sealer treated and then heavily sandblasted sectin 2 before performing the permeability test. The remaining section 2 cores were not altered. Each core had three or four 51-mm (2-in) thick disk sections available for the test. Initially, the two top disks from each core were used in the permeability tests. If needed, additional sliced disk samples will be used to fulfill the study objectives.



Table 1 provides rapid chloride permeability data on 42 sawed concrete disks from the 17 cores. Table 2 shows the average total charge passed through depths of 0 to 51 and 51 to 102 mm (0 to 2 and 2 to 4 in) for the five deck sections.

Discussion and Conclusions

The AASHTO T-277 procedure was developed to assess the quality of concrete matrix. Table 3, taken from the AASHTO procedure, shows total charge values established for 51-mm (2-in) thick disk samples of various concretes. [2] These values serve as a rough guide for interpreting the test data to determine the quality of untreated and sealer-treated disk samples.

Based on the test data and the information in table 3, the following conclusions about the tested sealer can be made.

1. When applied on a good quality concrete surface, this sodium-silicate-based sealer produced a slight--but not significant--reduction in permeability. The average permeability of the 17 disk samples measuring 0 to 51 mm (0 to 2 in) was 1,727 coulombs compared to 1,993 for the control (untreated) disk sections. Similarly, the average permeabilities of the 51- to 102-mm (2- to 4-in) samples and controls were 2,072 and 2,255 coulombs, respectively.

2. The sealer reduced the permeability of the concrete surface slightly more when it was sprayed rather than brushed on. The average permeability for deck sections 1 and 2 (wetted; sealer brus-applied) samples were 1,925 coulombs for the 0- to 51- mm (0- to 2-in) sections and 2,025 coulombs for the 51- to 102-mm (2- to 4-in) sections, respectively. In contrast, deck sections 5 (sprayed) had average permeabilities of 1,397 and 1,977 coulombs for the 0- to 51-mm (0- to 2-in) and 51- to 102-mm (2- to 4-in) sections, respectively.

3. The sealer penetrated less than 6.35 mm (0.25 in) into the concrete surface. The average permeability of the two sawed disk samples 6.35 to 57 mm (0.25 to 2.25 in) (top 6.35 mm [0.25 in] of concrete removed befure running the chloride permeability test) was 2,274 coulombs; in contrast, the control disk samples 0 to 51 mm (0 to 2 in) has an average permeability of 1,993 coulombs. Clearly, the sealer applied to the concrete surface did not penetrate into the concrete matrix.

4. The treated deck sections did not achieveda "very low" chloride permeability level. The quality of the untreated removed deck section showed that the concrete had a low water-cement ratio and a low chloride permeability with a value of about 2,000 coulombs. None of the sealer-treated disk samples achieved the very low permeability level of 100 to 1,000 coulombs as observed for latex-modified and internally sealed concretes.


[1] Standard Specifications for Transportation Materials and Methods of Sampling and Testing, Part I, "Specifications" and Part II," "Tests," (fifteenth edition), American Association of State Highway and Transportation Officials, Washington, DC, 1990.

[2] D. Whiting. "Rapid Determination on the Chloride Permeability of Concrete," Publication No. FHWA/RD-81/119, Federal Highway Administration, Washington, DC, August 1991.

Yash Paul Virmani is a research chemist in the Structures Division of the Office of Engineering and Highway Operations Research and Development, Federal Highway Administration. Dr. Virmani is the program manager for the Nationally Coordinated Program "Corrosion Protection" and High Priority Area "Prestressed Concrete Protection." He is the coinventor of conductive polymer concrete, a material that is the basis of several cathodic sysms.

Dennis Sixbey is a research materials engineer in the Materials Division of the Office of Engineering and Highway Operations Research and Development, Federal Highway Administration. Mr. Sixbey is a registered professional engineer in Virginia with 9 years of experience in soils, aggregates, concrete, and rapid nondestructive testing procedures.
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Author:Virmani, Yash Paul; Sixbey, Dennis G.
Publication:Public Roads
Date:Mar 1, 1992
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